Accessing parent function's variable in a child function called in the parent using python

In Python 3.4, I would like to call a child function, defined outside the parent function, that still has access to the parent function's scope (see example below). While I have named the functions parent and child in the example below for ease of viewing, the functions I am thinking of have very separate tasks and it makes more sense to define them separately. I am used to doing the following commonly in JavaScript:

def parent():
test = 0
child()

def child():
test += 1
print(test)

However, I simply get an error when executing the above code. I tried a second variation using the 'nonlocal' keyword that also failed:

def parent():
test = 0
child()

def child():
nonlocal test
test += 1
print(test)

The error message being 'no binding for nonlocal 'test' found'. Is this possible in python as it is in many other languages or is the only option the following (not preferred):

def parent():
test = 0

def child():
nonlocal test
test += 1
print(test)

child()

Edit: passing the parent's variable to the child function won't work in my use case as I need to modify the parent's variable.

Edit 2: The parent and child methods are already part of a class that doesn't really logically have an attribute of a counter. The counter is something internal to the two functions to keep track of node visits in a graph (see real example below):